Plaster layers are frequently applied to walls and in particular to the ceilings of rooms. Where applicable, the plaster material is applied directly to the unfinished walls and ceilings. In the case of walls and ceilings covered with panels, it is useful to apply a layer of plaster to the panels in order to form a continuous, level inside surface. The panels used have different compositions, depending on their function. For example, there are pre-coated fiber panels with a layer of plaster that is facing the room inside. Following the mounting of the panels, the joints between the panels are filled and a thin layer of plaster is applied to even out the area. However, the plaster layer can also be composed of two or more layers, wherein each plaster layer consists of at least one plaster compound with a main grain share. A system composed of a plaster layer on fiber panels achieves a sound-absorbing effect over a large frequency range, provided that open and/or continuous pores extend over the total layer thickness of the plaster layer, meaning from the surface layer facing the room to the region where the plaster layer adheres to the fiber panel.
The DE 196 14 296 C2 describes a plaster compound having relatively large intermediate spaces and/or pores as a result of grains that are for the most part similarly large and are positioned adjacent to each other in the plaster layer. The hardened plaster layer contains pores which ensure a good sound absorption and thus also a good thermal insulation. To prevent clogging of the pores, the grainy portion is composed of a large share of the main grains and a small share of the fine grains. In addition, using a small amount of binder prevents the pores from being clogged with binder, especially with binder membranes. A small amount of synthetic resin dispersion binder together with a small amount of thickening agent is used, so that the use of even a small amount of the binder will make it possible to achieve the flow characteristics required for a stable joining of the tightly packed main grain share. In the dried out state, the binder and the fine-grain share jointly form minimum bridges between these grains of the main grain share at the contact locations. The porosity of the plaster layer is in the range of 20 to 50 percent by volume and ensures low flow resistances throughout the plaster layer (80-240 rayls). A marble grain with narrow grain distribution in the range of 0.1 to 0.5 mm can form the main grain share. When using this grain size for the grain main grain share, it is possible to achieve an extremely smooth surface which resembles a gypsum surface. The cohesive and/or open pores have diameters somewhat smaller than the average grain size of the main grain share. A bright surface color is achieved for the hardened plaster layer by using a white marble grain.
With a plaster layer arranged on a fiber panel, the pores extending through the plaster layer guarantee a sound absorption over the complete, audible frequency range. Experiments have shown that a sound dissipation is achieved within the pores of the plaster layer and in the fiber panel, wherein the amount of attenuation in the two layers preferably varies for different frequency ranges. In addition, the membrane-type vibrating capacity of the plaster layer on the fiber panel also results in a clear deep-tone absorption.
The EP 1 484 294 B1 describes coated building panels where the panel element is a fiber mat or fiber panel and the plaster layer comprises porous particles, a silica binder, an organic polymer and xanthan as the thickening agent, wherein the porous particles have diameters ranging from 0.1 to 3 mm, preferably from 0.5 to 1 mm. An embodiment is described for which in addition to the cavities in the porous particles, cohesive and/or open pores with diameters somewhat smaller than the particle diameters are formed between the particles, thereby ensuring a strong sound absorption. To achieve a white surface, porous particles of tobermorite are preferably used (for example Circosil). Following the installation of the coated panels, a plaster compound as described in the DE 196 14 296 C2 can be applied as the cover layer, wherein the pores on the surface have somewhat smaller cross sections, corresponding to the grain size of the cover layer, than in the region of the layer underneath which contains somewhat larger porous particles.
Dirt emanating from the users of the rooms can reach the surface of the open-pore plaster layers according to the DE 196 14 296 C2 or the EP 1 484 294 B1 and/or the dirt particles carried along by the air can result in dirtying the surface. The dirt covers at least partial regions of the grains in the plaster surface. With dirty grains, the bright color is no longer visible, thereby leading to an impaired total impression of the plaster surface. Cleaning with a cleaning solution is not very promising because of the porosity since the cleaning liquid and therein absorbed dirt particles can enter the plaster layer through the pores. A dry rubbing off or grinding down of the particle layer would result in visible unevenness of the surface and to clogging of the pores with the ground-off material. Removing the dirty plaster layers and applying new plaster layers is very expensive and involved. If the open-pored plaster layers are coated with a standard paint coat, the pore surfaces are closed off and the sound-absorbing characteristic of the plaster layer and/or the composition of the fiber panel and plaster layer are essentially lost.